In my superhero world, there is a hero. Her name is Monica Fairson. She is able to generate force fields. What might be a plausible reason why Monica wouldn’t use her force fields as transportation, like a force field surf board?
Infrisios' options are good so i'll carry them on
Option 3: Perhaps Force Fields have no traction? she could stand on one, but would immediately slip straight off. they can stop things from passing through, but pushing against them would be like pushing against the slippiest ice you've ever experienced so as soon as the force-field moved it would move but wouldn't pull her along with it
Option 4: because it breaks the laws of motion, specifically Law 3, every action has an equal and opposite reaction. she cannot ride it as there is no propulsion pushing away from her to push her in the opposite direction.
Option 4a: this would also mean that if she "pushed" a force field out with her powers, then she would be pushing and then pulling on it when she attempted to stand on it so the forces would cancel out and she'd just drop to the floor
Option 5: it requires focus and concentration to form a force field. so is unable to do that when shes moving
Option 1: Force Fields do not affect her. Not just her own Force Fields, but Force Fields in general. If she tried to use one as a "Surf board", she'd fall through.
Option 2: Force Fields can't exist or are unstable close to her. They might flicker or warp.
For more ideas, it would be great if you could give more information about the Force Fields.
It's all relative
In this case the force fields exist in space relative to her rather than to anything else. So while she can use them for shielding, she can't use them to fly. To be able to fly she'd need to be able to place the field relative to the ground.
The force field is utterly unresponsive to external forces
To be used as a surf board it would need to exert return pressure from the water on the rider. It doesn't do this and would just plough straight on relative to the rider's momentum. Action has no reaction.
Let's make an experiment. Take a plank of wood : you can lift it, move it, beat someone with it, protect yourself with it... no, try to lift it while you are on the plank. That's hard, isn't it? even if you have enough force, you just can't lift yourself and use the plank of wood as a surf board.
Monica's superpower is not so different. She just control a kind of air plank. She can lift it, move it, beat someone with it, protect herself with it, but can't use force field as a surf board.
Her force field might work a bit like kevlar. Kevlar is great for stopping bullets, as it soaks up all their kinetic energy, but it's not so great at stopping knives, as the sharp edge sliding against it just cuts straight through. It's only fabric, after all.
So her force fields would be great at deflecting blows that hit them straight on, but the moment they're forced to grind against something (like the floor), they get damaged, or lose their integrity, and end up failing.
(Note: the picture I have in my head is of her skating along the ground on her force field, like in the City Escape level of Sonic Adventure 2. If you picture it more like the Silver Surfer's hoverboard, then this answer wouldn't work (but also please edit that information into the question).)
Are the force fields movable? If no you can only use them to create a static object like a ladder or a bridge, not a surf board.
Assuming that force fields are movable these could be the reasons why she can't surf them:
- She needs to focus a lot to create the force field. It's not uncommon that the caster needs to put most of his/her capability in maintain the force field active, even a static force field. In this case is not "technically impossible" to surf a force field, it only needs so much concentration that it's practically impossible to do both things (create the field and move fast avoiding obstacles).
- The force fields are "almost" solid. A force field is not like an adamantium wall but rather an incredibly dense "fluid" or a non-newtonian fluid. Therefore a force field can easily stop bullets and act as a wall if someone is running against it, but since it's a viscous fluid, over time objects will pierce it. Imagine it like an OObleck surfboard, you can use it as a shield but you can't stand over it.
- Even if you can create a magic surfboard, how are you supposed to move it? You need to create a surfboard AND a frictionless slope, then you can move by using gravity, or you need to provide another source of propulsion. The force field can move as a solid body or its movement is technically the creation of f.f. in one place and disruption of f.f. in another place? Since it's a field I imagine it as space's property that the caster can activate and deactivate where he/she wants but this means that the only way to "move" a f.f. is to play with f.f.'s shape and f.f. doesn't actually move.
- The reason why the caster can generate force fields actually makes he/she "immune" to them. It's up to you define the caster's origin and his/her source of power.